The Altmark incident had revealed the frailty of the neutrality of a small country which falls foul of the interests of two great powers. The Altmark was the 15,000-ton German supply ship which had ministered to the needs of Graf Spee in the South Atlantic ; since the action off the Uruguayan coast, she had lain low, her holds packed with three hundred British seamen captured from Graf Spee’s victims. Until mid-February 1940, the worried German admiralty had heard no sound from her, but on the fourteenth she signaled that she was about to enter northern Norwegian waters. In those waters she should be immune to enemy attack ; under The Hague Rules she was entitled to passage through them, for she was not a man-of-war but a naval auxiliary flying the flag of the German merchant marine. Such defensive armament as she had boasted in the Atlantic was properly stowed away below. The Norwegian picket boats interrogated her ; her captain denied the presence of any prisoners—the position in law would not have altered if he had admitted them—and the Altmark was allowed to proceed.
The Norwegians undertook to escort her, but in Berlin late on the sixteenth the admiralty began intercepting British naval signals which left no doubt but that an attempt was afoot to capture the Altmark even if it meant violating Norwegian neutral waters. By 6 A.M. next morning these fears were confirmed. A radio signal of the British commander to the admiralty in London had been decoded in Berlin : the British destroyer Cossack had been alongside the Altmark and he and his group were returning to Rosyth. By midday a full report of this incident was in Hitler’s hands, telephoned through by the legation in Oslo. Seeing the British force—a cruiser and six destroyers—closing in, the Altmark’s captain had sought refuge in Jossing Fjord. Two Norwegian vessels had held the British ships at bay until dusk, when the Cossack, her searchlights blazing, had forced her way past them into the fjord and ordered the German ship to heave to. The Altmark’s report described how a boarding party had seized the ship’s bridge “and began firing like blind maniacs into the German crew, who of course did not have a gun among them.” Six men died, many more were injured. A handful of the crew fled across the ice which hemmed the vessel in, or they sprang into the water ; the British boarders opened fire on these as well—an outrage to which the Norwegians also later testified. The three hundred prisoners were liberated, the ship and its crew were looted, and the Cossack withdrew. The Germans had not fired one shot.”
From David Irving, Hitler’s War.
You can also find the info on Norway and the Altmark in anything written about Admiral Raeder. My own info is from the Raeder and Ribbentrop defense cases at Nuremberg, volumes 14-16, mostly, but anything about the period ought to cover it, it’s very well known. Everybody protested Raeder’s imprisonment because everybody knew this. There’s also a book called RAEDER AT NUREMBERG, full of protests from military men from all over the world.